A polymer electrolyte fuel cell is, for example, a stack of a plurality of cells, each comprising a membrane/electrode assembly sandwiched between two separators. The membrane/electrode assembly comprises an anode and a cathode each having a catalyst layer, and a polymer electrolyte membrane disposed between the anode and the cathode.
The polymer electrolyte membrane in the membrane/electrode assembly is formed, for example, by applying and drying a liquid composition containing a polymer having ion exchange groups and a liquid medium. Further, the catalyst layer in the membrane/electrode assembly is formed, for example, by applying and drying a catalyst layer-forming coating liquid obtained by mixing the liquid composition and a catalyst.
The liquid composition is produced, for example, by a process comprising a step of extruding a fluorinated polymer having —SO2F groups in a melt state into a strand, which is cooled with water and cut by a pelletizer to obtain pellets, a step of converting the —SO2F groups in the fluorinated polymer having —SO2F groups in the pellets into ion exchange groups to obtain pellets of a fluorinated polymer having ion exchange groups, and a step of mixing the pellets of the fluorinated polymer having ion exchange groups and a liquid medium (Patent Document 1).